16:8 diet plan: what can you eat and what are the benefits?

You may have heard wonders about the 5:2 diet, but have you heard of the 16:8 yet?

clock with food on a pink background to represent intermittent fasting and the 16:8 diet

The 16:8 diet plan is one of the most popular ways to get into intermittent fasting, with big names like Jennifer Aniston and Hugh Jackman swearing by their successes. 

It's not only celebrity endorsement that has got this eating regime its reputation though. While not as restrictive as the 5:2 diet plan, clinical nutritionist Suzie Sawyer (opens in new tab) says, the 16:8 still prolongs "the period when your body has burned through calories consumed during your last meal and begins burning fat." In other words, it helps participants lose weight by reducing the amount of time they have available to eat - and so putting them into an energy deficit, which in turn helps them to lose weight.

All of this without the need to count calories or spend hours on a treadmill. But is the plan all it's really cracked up to be?

What is the 16:8 diet?

The 16:8 diet is a form of intermittent fasting where you break the day into two parts: a 16-hour and an 8-hour period. "People who follow this eating plan will fast for 16 hours a day (except for water and unsweetened soft drinks and infusions without added milk) and consume all of their calories during the remaining 8 hours. There are no restrictions on the types or amounts of food that a person can eat during the 8-hour window. This flexibility makes the plan relatively easy to follow," Suzie says. 

Designed to be a diet that works fast (opens in new tab), 16:8 stems from the 8-Hour Diet book by author David Zinczenko and Peter Moore, former editor-in-chief of Men's Health. The two created the plan off the back of popular 5:2 diet meal plans (opens in new tab) , with the main difference being the longer fasting time between eating sessions. This, they say, gives the body the time it needs to process food and burn away extra fat.

The 8-Hour Diet by David Zinczenko and Peter Moore - £6.16 | Amazon (opens in new tab)
Published in 2013, the 8-Hour Diet book has all the information, factoids, meal plans and tips for following through with the 16:8 diet.

How does the 16:8 diet work?

The 16:8 diet works on an hourly basis, so each day you eat within an 8-hour time frame and then fast for the remaining 16 hours. This works for weight loss as it "helps you eat fewer calories while boosting metabolism slightly," clinical nutritionist at Alive! (opens in new tab) Suzie Sawyer says. "It's a very effective tool to lose weight and visceral fat. After hours without food, the body exhausts its sugar stores and starts burning fat, sometimes referred to as 'metabolic switching'."

This switch is a natural process that happens when the body runs out of energy from food, research published in Nature (opens in new tab) explains. The body changes its energy source from glucose that's stored in the liver to ketones, which are stored in fat cells. While the body is getting its energy from glucose, it's maintaining or gaining weight and when the switch happens, it beings to lose weight.

However, calorie-restricted diets like Fast 800 (opens in new tab) work in a similar way. They push the body into a calorie deficit, forcing it to take its energy stores from fat cells rather than glucose. Research from the University of Illinois (opens in new tab) also suggests that when it comes to losing fat, the two are equally as effective as each other. So what's special about the 16:8 diet?

Unlike calorie-restricted diets, short-term intermittent fasting helps to speed up your metabolism - by as much as 14%, according to research from Johns Hopkins Weight Management Center (opens in new tab). It does this by causing a rise in norepinephrine, a stress hormone responsible for releasing fatty acids from fat cells and making larger amounts of fat available for the body to burn. And the faster your metabolic rate, the more calories you'll burn by doing basic activities like sitting down, eating and sleeping. Exercise is also encouraged during intermittent fasting, which in turn helps with hanging onto and building muscle mass - another essential way to boost your metabolism.

This style of eating is very different to most of the other diets out there, Suzie says, and that's why it works. "If you are someone who eats three meals a day, plus snacks, and you don't exercise much, then every time you eat, you are running on those calories and not burning your fat stores," she explains. "Intermittent fasting works by increasing the period when your body has burned through the calories eaten during your last meal and begins burning fat."

When can I eat on the 16:8 diet?

If you're following the 16:8 diet, you can pick any 8-hour window to suit your day. "The most common hours adopted for the eating period is 12pm to 8pm," explains Tom Jenane, nutrition and fitness expert at Nature's Health Box (opens in new tab). "The reason for this is because people aren't normally that hungry in the morning and you don't want to be consuming too many calories in the evening. This window allows for lunch and dinner as well as healthy snacks (opens in new tab)."

Person eating eggs and salmon for breakfast while on the 8 Hour diet

Credit: Getty
(Image credit: Getty Images)

But while the choice is yours when it comes to eating on the 16:8 diet, research has identified the best time to eat breakfast, lunch and dinner (opens in new tab) for weight loss. According to a study by University of Murcia (opens in new tab), it's best to stick to a breakfast in the morning as skipping the meal is linked to a higher rate of obesity. While a late lunch (after 3pm) can hinder weight loss in those trying to reduce fat mass. And a late dinner (within two hours before going to sleep) decreases glucose tolerance, making it easier to gain weight.

What can you eat on the 16:8 diet?

The great thing about the 16:8 diet is that you can eat anything you want - within reason. It's important to choose whole foods and those high in vitamins during the eating period. "Many people fail the 16:8 diet by packing in too many calories into the 8-hour period, often trying to get some in before the 8 hours ends. You should still be following a strict diet with a complete nutritional breakdown, to ensure you are consuming a targeted number of calories, not to mention macro nutrients and ensuring you’re not consuming too much sugar," says Tom.

Try sticking to the following foods on the 16:8 diet:

  • Whole grains: Ones like rice, oats, barley, wholegrain pasta and quinoa.
  • Protein: Meat, poultry, fish, eggs, nuts and seeds.
  • Fruit: Apples, bananas, berries, oranges and pears.
  • Vegetables: Broccoli, spinach and other leafy greens.
  • Healthy fats: Olive oil, coconut oil, avocados.

How much weight can you lose on the 16:8 diet?

To lose weight on the 16:8 diet, it's important to match the fasting with healthy eating and exercise. If done so correctly, there's a typical weight loss of around seven to 11 pounds over a ten week period, according to a review of studies by Sydney Medical School (opens in new tab). They found, on average, someone weighing 90kg would lose 5% of their body weight in 10 weeks.

But how much weight you lose on the 16:8 diet depends on eating fewer calories than you're burning. According to a leading study by the University of Vienna (opens in new tab), this energy deficit can be achieved in many ways - but is ultimately the only method of weight loss. When you eat food, your body metabolises it to create energy. This is used for daily activities - everything from breathing to walking around. If you have more energy than what your body burns, the extra is mainly stored as fat. If you have less energy than what your body burns, your body will turn to fat stores for energy. Aka. the calorie deficit.

While intermittent fasting has benefits, eating in a 8-hour period alone will not automatically mean you lose weight. The plan is just one way to achieve the deficit without having to count how many calories you burn in a day (opens in new tab). The given eating time aims to automatically restrict the amount of food you can eat, leading to weight loss.

How often should you do 16:8 intermittent fasting?

Unlike other intermittent fasting diets, each day of the 16:8 works independently to the other days. This means that technically you can do anywhere from one day of intermittent 16:8 fasting to seven days a week. It all depends on your goals and the advice from your GP.

Evidence differs, however, on whether it's healthy to do intermittent fasting all the time. While research from Queen's Medical Centre (opens in new tab) has proven that short-term fasting boosts the metabolism, longer fasts of around three or more days can actually suppress it and slow it right down. Plus, going without food for a long period of time can lead to an increased level of cholesterol, feeling sick in the morning (opens in new tab), dehydration and spells of low blood sugar.

Are there any health benefits to fasting?

“Apart from weight loss, there are other health benefits of following a 16:8 intermittent fasting eating regime," Suzie says. These include: 

Woman eating bread for lunch with family at the table

Credit: Getty
(Image credit: Getty Images/Maskot)

Making weight loss easier

Intermittent fasting can change the function of hormones, cells and genes, Suzie says. "Changes in hormone levels makes stored body fat more accessible and initiates important cellular repair processes. When you fast, insulin levels drop, and human growth hormone (HGH) increases. Your cells also initiate important cellular repair processes and change which genes they express."

Lowering the risk of type 2 diabetes

Anything that reduces insulin resistance should help lower blood sugar levels and protect against type 2 diabetes, she says. "Interestingly, intermittent fasting has been shown (opens in new tab) to have major benefits for insulin resistance and can lead to an impressive reduction in blood sugar levels."

Reducing stress and inflammation in the body

"Studies show that intermittent fasting can reduce oxidative damage and inflammation in the body. This should have benefits against ageing and development of numerous diseases, according to a study linked with the University of Toronto (opens in new tab)."

Improves heart health

"Intermittent fasting can improve numerous risk factors for heart disease. This includes blood pressure, cholesterol levels, triglycerides, and inflammatory markers," Suzie says. "However, much of this research has been done on animals and therefore needs to be studied more in-depth in humans."

Grace Walsh is a Features Writer for Goodto.com, covering breaking news health stories during the Covid-19 pandemic as well as lifestyle and entertainment topics.  She has worked in media since graduating from the University of Warwick in 2019 with a degree in Classical Civilisation and a year spent abroad in Italy. It was here that Grace caught the bug for journalism, after becoming involved in the university’s student newspaper and radio station.